CHEMICAL INHERITANCE 



ditions. Again, the thallus of a liverwort, such as 

 Marchantia, shows differences. If a young gemma 

 of the moss is exposed to light in a certain position, 

 the lighted side is destined to be the upper surface 

 for ever, and the opposite side to be for ever the 

 root-producing under surface. Nothing can change 

 this. Such a case corresponds to adaptation, it is 

 strictly hereditary, and must be called a purposive 

 reaction, because the proper tissues develop on 

 both the light-side and the under surface. 



We may be sure that thorough investigation of 

 chemical phenomena in life will certainly disclose 

 analogies. Most probably the self-steerage in the 

 production of enzymes belongs to a series of such 

 phenomena. On the other hand, the above- 

 mentioned formation in tropical plants of fats 

 of a high melting-point may be called a perfect 

 chemical adaptation. 



Phenomena of inheritance of chemical properties 

 are as well known as those of hereditary mor- 

 phological properties. We know only how far 

 morphological and chemical properties are in- 

 heritable together, and how far chemical pro- 

 perties separately are hereditary. Nevertheless, 

 examples of chemical varieties show that some- 

 times only one chemical characteristic varies, 

 and no other. The bitter almond shows no 

 difference from the sweet variety of almond, but 

 by the presence of amygdalin. This case of 

 heredity depends upon fecundation processes, 

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